In the UMTS (Universal Mobile Telecommunications System) network, the specifications of long term evolution (LTE) have been drafted for the purpose of further increasing high speed data rates, providing lower delays and so on (see non-patent literature 1).
In LTE, as multiple-access schemes, a scheme that is based on OFDMA (Orthogonal Frequency Division Multiple Access) is used in downlink channels (downlink), and a scheme that is based on SC-FDMA (Single Carrier Frequency Division Multiple Access) is used in uplink channels (uplink).
A successor system of LTE—referred to as “LTE-advanced” (and also referred to as “LTE-A”)—has been under study for the purpose of achieving further broadbandization and increased speed beyond LTE, and the specifications thereof have been drafted as LTE Rel. 10/11. Also, the system band of LTE Rel. 10/11 includes at least one component carrier (CC), where the LTE system band constitutes one unit. Such bundling of a plurality of CCs into a wide band is referred to as “carrier aggregation” (CA).
In LTE Rel. 12, which is a more advanced successor system of LTE, various scenarios to use a plurality of cells in different frequency bands (carriers) are under study. When a plurality of cells are formed by substantially the same radio base station, the above-described CA is applicable. On the other hand, a study is also in progress to employ dual connectivity (DC) when cells are formed by completely different radio base stations.